1. Technical Field
The invention relates to a semiconductor structure and a method for forming the same and more specifically to a contact pad structure and a method for forming the same.
2. Description of the Related Art
The demand of memory devices increases complying with a growth in market of the electronic products. There are several types of memory devices, such as volatile and non-volatile memory (NVM) devices.
The dynamic random access memory (DRAM) and the cache memory are volatile memories. Although a read access velocity of a volatile memory is fast, a non-volatile memory can be used as a hard disk since data stored in non-volatile memories will exist even when the current pinch off. According to read/write characteristic differences of memory devices, the non-volatile memory can be separated into read only memory (ROM) and flash memory. Recently, flash memory has been widely used in a variety of filed, such as cell phone, digital camera and MP3.
In order to increase a storage capacity of the memory in a limited memory volume, a three dimensional (3D) memory is developed. In a 3D memory, pitches between each of elements are smaller and an element density in an unit area of the 3D memory is larger.